1. Field of the Invention
The present invention relates to a sausage casing, consisting of an isotropic spun fleece which is free of binding agent, is welded, cemented or stitched in the longitudinal direction, and consists of at least one polyamide and is partially compressed. Further, the present invention relates to a process for the production of such a sausage casing and for its use as directed for packing with sausage products that are to be air-cured.
2. Description of the Prior Art
Raw sausages are known to the consumer, for example, as salami, saveloy, or servalat sausages. These are produced from mixtures comprising coarse to medium-fine ground beef, pork, bacon, pickled beef, and spices, without the addition of water. Once the sausage casings have been filled with the mixture which has been cooled to approximately -4.degree. C. and is for this reason very solid, the sausages are sweated for 1-2 days at approximately 18.degree.-25.degree. C. and at 98% relative humidity whereupon the characteristic red colour of the meat develops. Subsequently, the sausages are lightly smoked for approximately 3 days at 18.degree.-20.degree. C. and are then cured at a maximum temperature of 18.degree. C. for several weeks in a curing chamber with slight air circulation, whereupon they lose between 25-45% of their weight in the form of water.
During the filling process, great demands are placed on the strength and elasticity of the casings, especially if automated filling processes are used, since what is required is an even solid filling in a cylindrical shape that is free of bulges.
In order that the curing process can proceed unhindered, the sausage casings must permit the passage of water vapor so that when water from the sausage interior reaches the surface of the meat filling, it can diffuse immediately through the casing and then evaporate from the surface of the sausage. Of course, a corresponding contraction in volume is associated with this loss of water and this becomes apparent primarily in a reduction in the circumference of the sausage, which the casing should follow by shrinking to the same extent.
During the course of the curing process, the fat that is contained in the raw sausage becomes more and more mobile and, if the casing is porous, this will then emerge from the sausage and soon become rancid. Since this is unhygienic and bothersome when the sausage is being handled, the sausage casings should also be fat-tight as far as possible.
Apart from sausage casings produced from collagens, which because the material is related to gut, are particularly suitable, it has to date been a problem to combine the characteristics set out above in an optimal manner to provide sausage casings produced from synthetic materials and intended for the production of raw sausage.
Of the many attempts that have been made to replace natural gut for raw sausage by casings of synthetic materials, only very few have achieved a noteworthy share of the market. In addition to collagen sausage casings and those that are impregnated with collagens and/or gelatine, these include woven or similar textile fibre structures, notably fibre reinforced recycled cellulose sausage casings and, to a slightly lesser extent, stitched sausage casings of cotton material.
There has been no lack of attempts to use fleece-type materials as a basis for raw sausage casings, although up to now these have achieved no economic importance due to the serious shortcomings of such materials.
The first attempts to produce sausage casings of fleece-type materials were aimed at the use of such materials as casings for boiling sausages. According to these, DE-PS-No. 19 17 265, DE-OS No. 19 62 331, DE-OS No. 21 05 715, and DE-OS No. 21 54 972 propose fleece-type materials of synthetic staple fibres with the addition of collagen fibres and with a coating of PVDC that is impervious to water vapour.
The use of a spun fleece as a sausage casing was taught for the first time in DE-OS No. 21 28 613. Polyamides, polyolefins, and polyesters were proposed as the starting material. Mixtures of these fibres with skin fibres or cellulose products were also proposed. A disadvantage of this fleece material was the fact that when peeled off, the sausage skins "split"- i.e., when pulled off the sausage, they divided so that the inner layer, which had become joined to the sausage material, had to be picked off and removed in small pieces. In order to alleviate this situation, it was at first proposed to use a lacquering or impregnating process with film-forming polymers. Subsequently, DE-OS No. 24 37 781 proposed preventing this "splitting" by use of a thermomechanical treatment. In this treatment, the spun fleece was calendered when hot so that the individual fibres were retained but became welded or blended together at the crossover points.
DE-OS No. 23 30 774 describes a sausage casing of a staple fibre fleece of polyamide fibres and/or viscose fibres and/or acrylic fibres. This material is stated to be suitable for boiling sausage and for raw sausage.
DE-OS No. 30 29 028 also teaches a sausage casing for the production of raw sausage. It is preferred that this should consist of a thermally consolidated spun fleece of PA or PP fibres, with a wet strength of at least 30N and a wet stretch factor of at least 95% and preferably be impregnated with a 1:1 mixture of polyvinyl alcohol and gelatine, to form a continuous film after drying.
Of the above-cited sausage casings, however, none has ever been commercially available. It is thus obvious that these fleece-type casings for raw sausages still suffer from one or several of the following shortcomings:
1. Insufficient strength, which becomes apparent not so much in bursting during the filling process as in a lack of consistency in diameter. This is to say that on being filled, the casings expand permanently under the filling pressure and for this reason are of varying diameter along their length or even bulge in places.
2. Inadequate permeability with regard to water vapour, which results in the need for an extended drying period-this being the result of using fleece bonding agents or a thermo-mechanical consolidation process that is too intensive to prevent fraying or shredding.
3. Too little capacity for shrinkage, which results in shriveled sausages and also in the casing peeling in places.
4. Inadequate proof against grease, which allows the fat to escape and drip off during the course of the curing process.
5. Fraying, i.e., splitting of the fibres during skinning, caused by inadequate bonding within the fleece itself.